This application is based upon and claims the benefit of priority on the prior Japanese Application No. 2000-368980, filed on Dec. 4, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method such as a copying machine, a printer, etc. for forming images on such a medium as paper, etc. and more particularly, to an image forming apparatus designed to discharge a medium with the surface having a formed image downward.
2. Description of the Related Art
Generally, on such an image forming apparatus as a copying machine, a printer, etc., a latent image is formed on an image carrier by supplying a developer to the latent image and developing it. This developer image is transferred on a paper and fixed thereon by heating and pressurizing the transferred developer image.
For example, an image forming apparatus to discharge a paper with a developer image fixed thereon by conveying it along a curved conveying path is known. On this type of image forming apparatus having a curved conveying path, there may be caused such a defect that the image forming surface with a developer image just formed contacts a guide member, etc. on the conveying path and a streak is produced on the image. For this reason, in order to prevent such the defective image forming as mentioned above, various devices have been made on this type of apparatus.
For example, a both side printer that was disclosed in Japanese Laid-Open Patent Publication No. 2000-109275 has a curved conveying path 200 connecting a printer unit 201 and a paper converting unit 202 as shown in FIG. 1. The printer unit 201 is composed of: a paper supply section 211 that sends one sheet of paper at a time, an aligning portion 212 that takes a timing, a photosensitive drum that attaches a toner to an image to actualize it, a transferring roller 214 that transfers an image formed on the photosensitive drum 213 on a paper, a fixing unit 215 that fixes the toner image transferred on a paper by pressurizing and heating it, and a paper guide 216 that guides a paper discharged from the fixing unit 215 toward the paper converting unit 202 through the conveying path 200. The paper converting unit 202 has a paper guide 221 that guides a paper being conveyed from the printer unit 201 along the conveying path 200, a conveying roller 222 that conveys the paper that is guided by the paper guide 221, and a reversing roller 223 that changes the paper conveying direction.
In this apparatus, in order to prevent the surface of a paper on which an image is formed from contacting the paper guides 216 and 221 arranged at the outside of the curved conveying path when a paper is conveyed through the curved conveying path 200, the conveying speed of a paper in the paper converting unit 202 is made slightly faster than the conveying speed of a paper in the printer unit 201 and a paper is conveyed while it is constantly given with a tension.
However, in the apparatus that was disclosed in the above-mentioned Japanese Laid-Open Patent Publication, a tension is always given to a paper being conveyed between two units 201 and 202 and it is therefore considered that there is such a problem that, for example, the surface of the conveying roller 222 of the paper converting unit 202 contacts the surface of a paper and the conveying roller 222 is worn out. Furthermore, there is also such a problem that the leading edge of a paper having an image fixed in the fixing unit 215 is in the free stated until it arrives at the conveying roller 222, and therefore, it tends to contact the paper guides 216 and 221 and may streak on the image printed on the paper.
Further, since a paper passing on the conveying path is always given with a tension, an excessive tensile force is applied to a paper and in the case of a thin and soft paper, the paper can be easily torn out by a slight projection, if any, on the conveying path 200.
The present invention has been made in view of the above-mentioned points and it is an object to provide an image forming apparatus capable of suppressing wear of a paper conveying mechanism and firmly preventing defective image forming caused by the contact of component elements.
According to the present invention, an image forming apparatus is provided. This image forming apparatus comprises: an image forming unit configured to form an image on a first surface of a medium; a guide member that is curved to become convex against the first surface of the medium passed through the image forming unit; a conveying mechanism configured to convey the medium with the image toward a discharge unit by curving the medium along the guide member; and a controller configured to control the conveying speed by the conveying mechanism along the conveying direction of the medium by the conveying mechanism so as to make the conveying speed at the downstream side from the guide member slower than that at the upper stream side from the guide member.
Further, according to the present invention, an image forming method is provided. This image forming method comprises: forming an image on a first surface of a medium; conveying the medium on which the image is formed toward a discharge unit by curving the medium along a guide member that is curved to become convex against the first surface of the medium; and controlling the conveying speed of the medium along the conveying direction so as to make the conveying speed at the downstream side from the guide member slower than that at the upper stream side from the guide member.